This invention relates to the use of a block hydrogel as a coating and lubricating finish for a surgical suture or ligature.
As early as 1972, R. Perret and A. Skoulious, Makromol. Chem. 156, 143-156 (1972); Makromol. Chem. 162, 147-162 (1972); and Makromol. Chem. 162, 163-177 (1972) disclosed the synthesis and characterization of thermoplastic poly(caprolactone)-poly(ethylene oxide)-poly(caprolactone) (PCL-PEO-PCL) ABA triblock copolymers. The purification and crystallization behavior of these materials was extensively discussed. However, no mention was made as to the biodegradability of these polymers, their swelling behavior, or to any medical use such as suture materials or as suture coatings. Pitt and Schindler, U.S. Pat. No. 4,379,138 have published extensively on the biodegradability of PCL; therefore, the PCL-PEO-PCL triblock polymers should make attractive biodegradable hydrogel materials but this use was never mentioned.
Reed, Ph.D. Dissertation, Univ. of Liverpool (1978) has disclosed the synthesis of poly(lactide)-PEO-poly(lactide) (PLA-PEO-PLA) ABA triblock copolymers. The biodegradability of these materials was recognized; however, there was no mention of their potential hydrogel nature, or the use of these materials as suture coatings.
Casey, et al., U.S. Pat. No. 4,452,973 (6/5/84) disclosed the synthesis of poly(glycolic acid)-PEO-poly(glycolic acid) (PGA-PEO-PGA) thermoplastic biodegradable ABA triblock polymers. The intended use for these materials was as absorbable sutures having the required flexibility for use as a monofilament. The patent discloses the use of trimethylene carbonate in combination with glycolide to prepare the A portion of the ABA triblock polymer.
Churchill, et al., U.S. Pat. No. 4,526,938 (9/2/85) also disclosed the use of degradable ABA triblock polymers as hydrogels. In this case, the middle block was also PEO and the endblocks were generally PLA or PLA/PGA copolymers although the use of PGA, PCL or poly(3-hydroxy-butyric acid) was mentioned with no specific experimental details given. No mention was made to using Gly/TMC endblocks for these hydrogels, or to using these materials as suture coatings.
Mattei (U.S. Pat. No. 4,027,676 to Ethicon, June 7, 1977) has disclosed suture coatings consisting of blends of absorbable copolymers of glycolide and lactide as a film forming resin, polyalkylene glycols as a lubricant, and a hydrophobic material such as a fatty acid or an ester of a fatty acid to improve tie-down performance. However, no mention was made of using block polymers formed from poly(alkylene glycols) and absorbable polymers. A particular disadvantage of the Mattei method of using blends of poly(alkylene glycols) with absorbable copolymers is the tendency for the poly(alkylene glycols) to dissolve prematurely if exposed to an aqueous environment (see, e.g., Example 4 of U.S. Pat. No. 4,027,676) rendering the coating less effective.
Mattei (U.S. Pat. No. 4,201,216 to Ethicon May 6, 1980) has also disclosed the use of an absorbable copolymer of glycolide and lactide as a film former blended with salts of C.sub.6 or higher fatty acids as suture coatings. No mention was made of using block polymers with poly(alkylene glycols) for this application.
Mattei has also disclosed the use of polyvalent metal fatty acid salt gels as suture coating materials (U.S. Pat. No. 4,185,637 to Ethicon Jan. 29, 1980). No mention is made of using block copolymers of poly(alkylene glycols) for this application.
Conventional hydrogels which are made by crosslinking water soluble polymers have several drawbacks which are associated with their crosslinked nature. These include a lack of both solubility and processability. In contrast the block copolymers of this invention are thermoplastic. They are soluble in common organic solvents and are fusible.
The biodegradable thermoplastic hydrogels of this invention are useful as a suture coating material for surgical sutures or ligatures. Their solubility in common organic solvents allows for a coating composition to be applied by conventional solution techniques. When applied in this manner the coating polymer will improve tie-down performance and lubricity of the surgical suture as compared to an identical uncoated surgical suture. The polymers of this invention will also degrade to non-toxic low molecular weight materials capable of being eliminated from the body without adverse reaction or response.
A bioabsorbable coating for a surgical suture or ligature comprising a diblock copolymer has been invented. The copolymer has a first block comprising a polyalkylene oxide and a second block consisting essentially of glycolic acid ester and trimethylene carbonate linkages. In one embodiment, the polyalkylene oxide block is from 5 to 25 percent by weight of the copolymer. In another embodiment, the number average molecular weight of the polyalkylene oxide block is from about 4,000 to 30,000. In yet another embodiment, the polyalkylene oxide block is derived from a polyalkylene oxide terminated on one end by a C.sub.1 to C.sub.6 alkyl group and on the other end by a hydroxyl group.
In a specific embodiment of any of the above embodiments, the polyalkylene oxide block is derived from a homopolymer of ethylene oxide. In another specific embodiment of any of the above, the polyalkylene oxide block is derived from a block or random copolymer of ethylene oxide and a cyclic ether. In a more specific embodiment, the cyclic ether is selected from the group consisting of ##STR1## wherein x is 2 to about 9, y is 1 to about 9 and R is a C.sub.1 to C.sub.6 alkyl group.
In yet another specific embodiment, the polyalkylene oxide block is derived from a block or random copolymer of a first cyclic ether selected from the group consisting of ##STR2## wherein x is 2 to about 9, and a second cyclic ether selected from the group consisting of ##STR3## wherein y is 1 to about 9 and R is a C.sub.1 to C.sub.6 alkyl group.
In a more specific embodiment (to the above specific embodiments), the inherent viscosity of the diblock copolymer, as measured at 30.degree. C. for a 0.5% (w/v) solution in chloroform or methylene chloride, is 0.25 to about 1.50 dl/g.
In a still further embodiment, the surgical suture or ligature containing the bioabsorbable diblock copolymer coating is also bioabsorbable. The suture or ligature is manufactured from a polymer. The polymer is prepared from one or more monomers selected from the group consisting of lactides. In one embodiment, the suture or ligature is manufactured from a homopolymer prepared from the monomer glycolide. In another embodiment, the suture or ligature is manufactured from a copolymer prepared from the monomers glycolide and lactide. In a specific embodiment, the suture or ligature is in multifilamentary form. In a more specific embodiment, the coating comprises about 1/10 to 5% by weight of the coated suture or ligature. In a most specific embodiment, the coating comprises about 1 to 3% by weight of the coated suture or ligature.
A bioabsorbable coating for a surgical suture or ligature comprising a triblock copolymer has also been invented. The middle block (of the triblock copolymer) is obtained by removing both terminal hydroxyl hydrogens either form a homopolymer of ethylene oxide, or from a block or random copolymer of ethylene oxide and a cyclic ether. In one embodiment, the cyclic ether is selected from the group consisting of ##STR4## wherein x is 2 to about 9, y is 1 to about 9 and R is a C.sub.1 to C.sub.6 alkyl group. In a specific embodiment, the middle block is obtained from a block copolymer of ethylene oxide and a cyclic ether of the formula: ##STR5##
Further, a bioabsorbable coating for a surgical suture or ligature comprising an alternative triblock copolymer has been invented. The middle block is obtained by removing both terminal hydroxyl hydrogens from a block or random copolymer of a first cyclic ether selected from the group consisting of ##STR6## wherein x is 2 to about 9, and a second cyclic ether selected from the group consisting of ##STR7## wherein y is 1 to about 9 and R is a C.sub.1 to C.sub.6 alkyl group.
In a further embodiment of any of the above embodiments, each end block of the triblock copolymer consists essentially of glycolic acid ester and trimethylene carbonate linkages. In a specific embodiment, the middle block is from 5 to 25 percent by weight of the copolymer. In a more specific embodiment, the number average molecular weight of the middle block is from about 4,000 to 30,000.
In a most specific embodiment (to the above specific embodiments), the inherent viscosity of the copolymer, as measured at 30.degree. C. for a 0.5% (w/v) solution in chloroform or methylene chloride, is 0.25 to about 1.50 dl/g. In a still further embodiment, the surgical suture or ligature containing the bioabsorbable bioabsorbable triblock copolymer coating is also bioabsorbable. The suture or ligature is manufactured from a polymer. The polymer is prepared from one or more monomers selected from the group consisting of lactides. In one embodiment, the suture or ligature is manufactured from a homopolymer prepared from the monomer glycolide. In another embodiment, the suture or ligature is manufactured from a copolymer prepared from the monomers glycolide and lactide.
In a specific embodiment, the suture or ligature is in multifilamentary form. In a more specific embodiment, the coating comprises about 1/10 to 5% by weight of the coated suture or ligature. In a most specific embodiment, the coating comprises about 1 to 3% by weight of the coated suture or ligature.